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Geothermal - Lincoln public schools - O+M

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SE-99-20-04Comparing Maintenance Costs ofGeothermal Heat Pump Systems with OtherHVAC Systems in Lincoln PublicSchools: Repair, Service, and CorrectiveActionsMichaela A. Martin, P.E. David J. Durfee Patrick J. Hughes, P.E.Member ASHRAE Member ASHRAEABSTRACT INTRODUCTION The Lincoln Public School District, in Lincoln, Geothermal ͑ground-coupled͒ heat pump ͑GHP͒Nebraska, recently installed vertical-bore geothermal heat systems installed in four new ͑1995͒ elementary schools inpump systems in four new elementary schools. Because the Lincoln, Nebraska have been found to be among the lowestdistrict has consistent maintenance records and procedures, consumers of total energy of over ﬁfty schools located withinit was possible to study repair, service, and corrective main- the district. Speciﬁcally, the average annual source energytenance requests for 20 schools in the district. Each school consumed by the GHP schools is 93.7 kBtu/ft2 ͑Martin 1999͒ whereas the only other schools to provide cooling for 100%studied provides cooling to over 70% of its total ﬂoor area of their ﬂoor area consume an average of 132.5 kBtu/ft2. Inand uses one of the following heating and cooling systems: conjunction with a study of the energy consumption of all ofvertical-bore geothermal heat pumps (GHPs), air-cooled Lincoln’s schools, a review of their maintenance requestchiller with gas-ﬁred hot water boiler (ACC/GHWB), water- database was performed in an effort to learn more aboutcooled chiller with gas-ﬁred hot water boiler (WCC/GHWB), actual maintenance costs for GHPs, and to compare theseor water-cooled chiller with gas-ﬁred steam boiler (WCC/ with more conventional HVAC systems found in the district.GSB). Preventative maintenance and capital renewal activi- Recently, a study of the annual maintenance costs for 25ties were not included in the available database. GHP buildings with GHP systems was conducted ͑Cane et al.schools reported average total costs at 2.13 ¢/ f t 2 -yr, 1998͒. This study focused on maintenance activities consid-followed by ACC/GHWB schools at 2.884 ¢/ f t 2 -yr, ered to be either responses to failures ͑repair or service͒ orWCC/GSB schools at 3.73 ¢/ f t 2 -yr, and WCC/GHWB those that were part of a planned maintenance programschools at 6.07 ¢/ f t 2 -yr. Because of tax exemptions on ͑preventative and corrective͒. The sample included 15material purchases, a reliance on in-house labor, and the schools, three ofﬁces, four multi-family homes, two ware-absence of preventative maintenance records in the database, houses, and one restaurant. Average annual costs ranged from 9.3 ¢/ft2 for in-house labor, to 10.95 ¢/ft2 for contractedthese costs are lower than those reported in previous studies. work. More speciﬁcally, average annual maintenance costsA strong relationship (R 2 ϭ0.52) was found between costs for schools ranged from 4.69 ¢/ft2 for in-house work, toexamined and cooling system age: the newer the cooling 6.97 ¢/ft2 for contracted labor. The age of these schoolsequipment, the less it costs to maintain. ranged from three to 17 years, with an average age of 6.2 years.Michaela A. Martin is a staff engineer at Oak Ridge National Laboratory, Oak Ridge, TN. David J. Durfee is a research associate at theUniversity of Tennessee, Knoxville, TN. Patrick J. Hughes is program manager at Oak Ridge National Laboratory, Oak Ridge, TN.THIS PREPRINT IS FOR DISCUSSION PURPOSES ONLY, FOR INCLUSION IN ASHRAE TRANSACTIONS 1999, V. 105, Pt. 2. Not to be reprinted in whole orin part without written permission of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., 1791 Tullie Circle, NE, Atlanta, GA 30329.Opinions, ﬁndings, conclusions, or recommendations expressed in this paper are those of the author(s) and do not necessarily reﬂect the views of ASHRAE. Writtenquestions and comments regarding this paper should be received at ASHRAE no later than July 7, 1999.

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TABLE 1 Data Collected to Establish School Characteristics Database Building Data Original Floor Area ft2 Original Age Year Number of Additions # Additional Floor Area ft2 Number of Portables # Portable Floor Area ft2 Total Floor Area ft2 Primary Cooling Primary Cooling Equipment Type Age of Primary Cooling Plant Year Portion of Floor Area Served % Rated Output Capacity Tons Secondary Cooling Secondary Cooling Equipment Type Age of Secondary Cooling Plant Year Portion of Floor Area Served % Rated Output Capacity Tons Primary Heating Primary Heating Equipment Type Age of Primary Heating Plant Year Portion of Floor Area Served % Rated Output Capacity MMBtuh, BHP, kW Secondary Heating Secondary Heating Equipment Type Age of Secondary Heating Plant Year Portion of Floor Area Served % Rated Output Capacity MMBtuh, BHP, kW Primary Distribution Primary Distribution Equipment Type Age of Primary Distribution Plant Year Portion of Floor Area Served %Secondary Distribution Secondary Distribution Equipment Type Age of Secondary Distribution Plant Year Portion of Floor Area Served % An older study of conventional HVAC systems was the database, it was clear that not all maintenance activitiescommissioned by ASHRAE ͑Dohrmann et al. 1986͒ and is are included. Speciﬁcally, planned preventative actions arethe basis for the maintenance costs listed in the 1995 HVAC often scheduled by less formal methods and not always foundApplications Handbook ͑ASHRAE 1995͒. This early study in the database. Therefore, the majority of the data containedcontained a sample of 342 commercial buildings, located in this database covers mainly actions that are repair andacross the U.S., of ages ranging from two to over 25 years service responses to equipment failures, or are considered toold. Multiple system types were included, but not GHPs, be corrective maintenance ͑ASHRAE 1987͒. This studywhich were not commonly available at the time. Average summarizes the maintenance data from 20 schools, with aannual maintenance costs for the entire sample were 32 ¢/ft2, focus on the unplanned actions required at the schoolswith a median cost of 24 ¢/ft2. utilizing GHPs. Each school studied provides cooling to over In consideration of the approaches used, and results 70% of its total ﬂoor area, and uses one of the followingobtained from these two previous studies, a review of the heating and cooling systems: vertical-bore geothermal heatmaintenance effort at Lincoln Public Schools ͑LPS͒ is pumps ͑GHPs͒, air-cooled chiller with gas-ﬁred hot waterunderway. The ﬁrst component of this review is the analysis boiler ͑ACC/GHWB͒, water-cooled chiller with gas-ﬁred hotof a two-year database of maintenance requests for all water boiler ͑WCC/GHWB͒, or water-cooled chiller withschools within the district. Following a preliminary review of gas-ﬁred steam boiler ͑WCC/GSB͒.2 SE-99-20-04

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BACKGROUND ON AVAILABLE DATA maintenance laborers and $27.30 for skilled workers. Including workers compensation and overhead, the national In order to compare HVAC system maintenance costs common and skilled labor rates are $21.14 and $36.85,for all schools in the Lincoln District, an understanding of the respectively. Labor costs presented here are normalized to aphysical characteristics and equipment installed at each national basis and include fringes, workers compensation,school was necessary. Characteristics, such as ﬂoor area, and overhead.facility age and number of additions, and HVAC system In addition to labor rates, hours, and costs, the databasetypes, capacities, and commissioning dates were provided by provides information on material costs. Because the schoolthe district. Table 1 lists the categories of data collected for district enjoys tax-exempt status, the material costs providedthe building characteristics database. Table 2 provides a basic do not include any form of sales tax.summary of building and system data for schools with thefour systems studied. Characteristics records indicate a range SUMMARY OF RESULTSof total ﬂoor areas from 22,150 ft2 to 367,826 ft2, school agesfrom three to 75 years, cooling plant ages from two to 32 Tables 3 and 4 summarize labor hours, labor costs,years, and heating plant ages from three to 70 years. material costs, and total costs for schools utilizing the four The school district maintains a database of maintenance groups of HVAC systems studied. Table 3 speciﬁcallyrequests that were submitted within the past 2–3 years for all presents this information on a per request basis, while the data in Table 4 are presented on an annual basis. Thesefacilities within the district. Maintenance records include the results represent a two to three year snapshot of repair,date of request, date of completion, request category ͑or work service, and corrective maintenance actions taken during thecodes͒, craft͑s͒ requested, labor rates, hours and costs, mate- lifetime of the installed equipment.rial costs, and a brief description of the problem. The data- Database records indicate that, by their third year ofbase contains over 300 work codes that identify the category operation, individual repair, service, and corrective mainte-of request. Examples of work codes include heating, cooling, nance requests by the GHP systems are less costly than thoseEnergy Management System ͑EMS͒, plumbing, and tele- reported for the conventional systems of various ages ͑Tablephone repair. Based on a query performed by the school 3͒. The average labor effort required per GHP request was 2district, over 7,600 maintenance requests using HVAC-re- hours, with a labor cost of $47. While GHP labor costs perlated work codes were identiﬁed. request are only slightly lower than the average reported for Of the original 7,600 maintenance records categorized WCC/GHWB systems ͑$53͒, material costs per GHP requestunder HVAC work codes, 2,934 were veriﬁed as legitimate at $29 are well below those for ACC/GHWB systems at $79.HVAC-related activities. A record-by-record review of the Average per request material costs are highest for WCC/GSBHVAC-related requests provided by the district found that systems at $122. As a result, GHP schools reported lowermany labeled as HVAC work codes were actually concerned average total costs per request at $77, followed bywith water fountain or restroom repairs. This veriﬁcation ACC/GHWB schools at $153, WCC/GHWB schools at $157,process also determined that the database requests for main- and WCC/GSB schools at $253.tenance actions were mainly repair and service responses to On an annual cost basis, combined labor and materialequipment failures, or corrective maintenance. Planned costs for repair, service, and corrective actions are lower, onactions, such as preventative maintenance, are not included in average, for GHP systems than for the three other systemsthe database, nor were any capital renewal projects for studied ͑Table 4͒. Average annual labor effort and labor costscomplete replacement of older HVAC equipment. Following reported for the GHP systems, at 43 hours and $937, areveriﬁcation, the data were then subdivided by school and competitive with the average for WCC/GHWB systems, atexamined. 52 hours and $1,142. Average total labor effort and costs are The majority of the database requests indicate that most highest for the WCC/GSB schools at 121 hours and $2,703work was performed by in-house LPS labor. Lincoln relies per year. Similar to the per request comparison, average totalheavily on its in-house work force to handle most mainte- annual costs are lowest for GHP schools as a result of lowernance jobs and rarely uses contractors. Additionally, because material costs. GHP schools reported lower average totaltheir ﬁrst-year system warranties had expired, all GHP annual costs at $1,508, followed by ACC/GHWB schools atrequests were completed by in-house staff. The average $2,870, WCC/GHWB schools at $3,250, and WCC/GSBin-house base wage ͑including fringes͒ reported for HVAC schools at $6,487.requests is $14 per hour. Maintenance requests may be The commonly recognized method to compare costshandled by a variety of skill levels, depending on the require- from one case to the next uses an area-normalized basis.ments of the task. On-site custodians, mechanical equipment Annual reported average total costs per square foot of ﬂoortechnicians ͑based at all high schools͒, and mobile craft area are lowest for GHP systems. GHP schools reported totalspecialists have base labor rates, including fringes, that range average repair, service, and corrective maintenance costs atfrom $13.50 to $18.75 per hour. The corresponding national 2.13 ¢/ft2-yr, followed by ACC/GHWB schools ataverages for in-house base labor rates ͑Means 1998͒, 2.88 ¢/ft2-yr, WCC/GSB schools at 3.73 ¢/ft2-yr, andincluding fringes, are slightly higher at $15.50 for common WCC/GHWB schools at 6.07 ¢/ft2-yr. A review of theSE-99-20-04 3

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building characteristics data seems to indicate that a linear reprogramming, replacement batteries, and communicationrelationship exists between these aggregated costs and problems. The other major work codes, pump repair, boilercooling system age. While no relationship exists between the repair, and ventilation repair, are more clearly deﬁned.heating system age and these aggregated costs (R 2 →0), a A closer look at the details of GHP requests indicatestatistically signiﬁcant linear relationship does exist between several common, recurring equipment, design and installa-cooling system age and costs ͑R 2 ϭ0.52, pϽ0.05͒. Figure 1 tion problems. The most common problem, which is actuallyillustrates the linear dependence of aggregated repair, an application ﬂaw, is leakage found in the packing of motor-service, and corrective maintenance costs on cooling system ized two-way ball valves located at each heat pump. Theage. two-way valves isolate the unit when not in operation and are Compared with the aforementioned ASHRAE-spon- part of the variable ﬂow design of the water loop. Ball valvessored maintenance studies, the maintenance costs reported by with external actuators were selected over solenoids as a costLincoln seem low. There are several reasons for this, saving measure. It is hypothesized that either the externalincluding Lincoln’s dependence on in-house labor instead ofcontracted labor, a sales tax exemption on materialpurchases, and the inclusion of other building types in the TABLE 5original ASHRAE maintenance study. Additionally, because Top Five Work Codes Cited for Repair, Service,these costs do not include preventative maintenance actions, and Corrective Maintenance Actions. Data Do Nota complete maintenance picture is not presented. An effort is Include Preventative Maintenance or Capitalpresently underway to collect data from the school district Renewal Actionsregarding typical preventative maintenance efforts and costs Group A: Geothermal Heat Pumps „Vertical-Bore…required by each system type. Further, this interim analysisbased on the maintenance request database does not recog- Total Calls Per Year Calls per Year pernize the fact that the school district payroll includes all main- Work Code ͑4 schools͒ Schooltenance staff as full-time employees whether or not their timeis fully accounted for in the database. An effort is presently Heating 20 5underway to fully account for all of Lincoln’s actual main- Air Conditioning 10 2.5tenance costs, and when completed the values are expected to Pump Repair 9 2.25be comparable to the previous work. Controls 9 2.25 The top ﬁve work codes listed for each system type are EMS Equipment 6 1.5presented in Table 5. Clearly there exists some overlapbetween work codes as well as deﬁnitions that are extremely Group B: Air-Cooled Chiller and Gas-Fired Hot Water Boilergeneral in nature, however there is some value in the gener- Total Calls Per Year Calls per Year peralizations. Selection of appropriate work codes is dependent Work Code ͑2 schools͒ Schoolon the requestor, and thus gray areas exist between codes. Air Conditioning 6 3Requests listed under heating and air conditioning generally EMS Equipment 6 3pertain to problems with the plant and air-handling equip- Controls 4 4ment, but also include complaints of ‘‘room too cold’’ or Boiler Repair 5 2.5‘‘room too hot.’’ EMS and control requests are similar in that Group C: Water-Cooled Chiller and Gas-Fired Steam Boilerboth list issues with thermostats or comfort complaints.Many requests under EMS, however, speciﬁcally mention Total Calls Per Year Calls per Year per Work Code ͑2 schools͒ School Controls 9 4.5 Air Conditioning 8 4 Ventilation 5 2.5 Heating 4 2 Boiler Repair 4 2 Group D: Water-Cooled Chiller and Gas-Fired Hot Water Boiler Total Calls Per Year Calls per Year per Work Code ͑12 schools͒ School Controls 60 5 Heating 29 2.4 Boiler Repair 27 2.25 Air Conditioning 22 1.8Figure 1 Relationship between aggregated repair, service, and Ventilation 16 1.3 corrective maintenance costs and cooling system age.SE-99-20-04 7

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actuators torque the valve stems such that the packing leaks, schools at 6.07 ¢/ft2-yr. A relationship does exist betweenor that the valves were intended for manual operation and these costs and the age of the cooling system, and at anlimited cycles. Most of the actuators have been disengaged average age of three years, the four GHP systems studied areand the valves left in the open position. Another source of among the youngest in the district. These costs are low inleakage from the GHP units themselves reportedly came comparison with those found in other studies, as most of thefrom the condensate lines or drip pans. Condensate leaks may work was completed by in-house labor ͑as opposed tobe caused by problems such as unlevel mounting of units, contracted labor͒, material costs were tax-exempt, andfailure to ﬂush lines with biocide to prevent clogs, unit preventative maintenance actions were not included in thedamage during shipping or at the site, poor mounting of the database ͑the district handles these less formally͒. The nextcondensate drip pan, or pinched hoses. Several occurrences phase of this study will attempt to develop total maintenanceof water leakage at the loop central pumping station were costs by quantifying preventative maintenance activities andalso reported. Like the schools with conventional systems, all associated costs and capital renewal requirements for olderGHP schools reported common thermostat, freezestat, or HVAC systems throughout the district.other control-related issues, in addition to EMS alarms forGHP unit shutdowns. Filter racks and/or access doors were ACKNOWLEDGMENTSadded to many of the heat pumps to make ﬁlter changes and The authors wish to recognize the following representa-servicing easier for personnel. Finally, a handful of requests tives of the school district who have generously shared theirwere received to repair heat pump vibration or noise. time, data, and experience: Larry Hennings, Tim Pratt, Julie Many of the requests listed for the GHP systems identify Kleager, and Brent Adams.concerns that have been commonly expressed by designers,contractors, and those considering GHPs as an alternative to REFERENCESmore conventional heating and cooling equipment. While the ASHRAE. 1987. HVAC Systems and Applications Hand-existence of these issues in this database supports such book. Chapter 59. Atlanta, GA: ASHRAE.concerns, it is obvious that many of the problems could have ASHRAE. 1995. HVAC Applications Handbook. Chapter 33.been avoided with improvements in application and/or instal- Atlanta, GA: ASHRAE.lation. Additionally, as is evident in the cost summary data, Cane, D., A. Morrison, and C. Ireland. 1998a. Maintenanceresolution of these problems proved to be inexpensive as and service costs of commercial building ground-sourcemaintenance actions were completed quickly with low-cost heat pump systems. ASHRAE Transactions 104͑2͒.materials by less-skilled laborers. Cane, D., A. Morrison, and C. Ireland. 1998b. OperatingCONCLUSIONS experiences with commercial ground-source heat pumps—Part 2. ASHRAE Transactions 104͑2͒. Based on a two to three year snapshot of maintenance Dohrmann, D. and T. Alereza. 1986. Analysis of survey datarequests recorded in the Lincoln Schools maintenance data- on HVAC maintenance costs. ASHRAE Transactionsbase, four schools heated and cooled with vertical-bore 92͑2A͒.geothermal heat pumps were found to have the lowest Martin, M., J. Shonder, T. Sharp, D. Durfee, and P. Hughes.average annual repair, service, and corrective maintenance 1999. Benchmark for performance: Geothermal applica-costs, per square foot, when compared to sixteen other tions in Lincoln Public Schools. ASHRAE Transactionsschools utilizing three other types of conventional HVAC 105͑2͒.systems. GHP schools had average costs of 2.13 ¢/ft2-yr, in Means, R. S. 1998. Facilities maintenance and repair costcomparison to ACC/GHWB schools at 2.88 ¢/ft2-yr, data. First Edition. Kingston, MA: R.S. MeansWCC/GSB schools at 3.73 ¢/ft2-yr, and WCC/GHWB Company, Inc.8 SE-99-20-04